Known in the art is the use of a so-called wastegate in exhaust gas turbochargers of internal combustion engines to regulate the charge air. The wastegate of a wastegate valve arrangement is usually a simple flap with which the quantity of exhaust gas flowing over the exhaust turbine of an exhaust gas turbocharger is regulated by means of an electrical actuator. Such actuators are connected with the wastegate by a connecting rod or push rod routed out of a housing. In such actuators, values of up to approx. 250 N may be required in the connecting rod to keep the wastegate in a closed position. These forces must be permanently provided in order to reliably keep the wastegate in the closed position, so that the wastegate remains tight despite the opposing forces of the exhaust gas.
Known from DE 10 2008 051 818 A1 is a method for controlling a wastegate situated in a bypass channel for a turbine of an exhaust gas turbocharger by means of an electrical actuator, in which an exhaust gas flow of an internal combustion engine can be routed past the turbine or completely on the turbine via the bypass channel by opening or closing the wastegate. When the internal combustion engine is under a load, the wastegate is closed and pressed against a wastegate valve seat with a predetermined first force, wherein this predetermined first force is selected in such a way that the bypass channel remains tightly sealed in terms of flow against the pressure exerted by the exhaust gas of the internal combustion engine during exposure to the load and at least until a desired torque is reached. In addition, this known method provides that, with the internal combustion engine under a partial load, the wastegate is closed and pressed against the wastegate valve seat with a predetermined second force, wherein the predetermined second force is less than the predetermined first force. The predetermined first force is generated by supplying a maximum holding current to the electrical actuator. Reducing this holding current that determines the first force to a second lower value helps protect the servomotor of the electrical actuator against overheating.
In this known method, preset current strength values for the electric motor of the electrical actuator are used to generate a specific respective closing force on the wastegate, wherein the higher value is generated when the internal combustion engine is under a load or exhibits a transient operating behavior, and the lower value is generated under a partial load. However, the disadvantage is that the higher value must be selected in such a way that the wastegate tightly seals the bypass channel under all arising operating conditions, in particular given a transient operation of the internal combustion engine, i.e., in an acceleration process or given rapidly switching loads, during which arising pressure pulsations of the exhaust gas make it possible to briefly press open the wastegate. As a result, even under operating conditions where the force required to tightly close the wastegate could be met with lower current values, the servomotor is unnecessarily exposed to what is then an excessive maximum or potentially also distinctly too high a level of force.
Since forces far in excess of 250 N are reached in the push rods of actuators for wastegates, there is a danger that, given the constant generation of a closing force as proposed by the method according to DE 10 2008 051 818 A1, such forces will cause damage to the exhaust gas turbocharger or its housing and lead to increased wear, since, for example given a wastegate that can be activated via a push rod, the actuating forces generated in this push rod result in reactive forces in the housing.
DE 10 2009 028 117 A1 further describes a method for operating an electrical actuator for a wastegate actuating device of an exhaust gas turbocharger, in which a wastegate can be electrically adjusted with the help of the actuator and is situated in an exhaust gas system of an internal combustion engine, wherein a quantity of exhaust gas flowing through the exhaust gas turbocharger can be set as a function of an open position of the wastegate. In this method, the actuator is exposed to an electrical current with the wastegate in a closed position, so as to generate a varying closing force corresponding to the progression of an exhaust gas back pressure applied over the wastegate. The actuator can here be activated in such a way that the closing force is essentially proportional over time to the exhaust gas back pressure or chronologically offset in its proportionality relative thereto. Since the chronological progression of the exhaust gas back pressure depends on the crankshaft position of a crankshaft in the internal combustion engine, current is supplied to the actuator as a function of the crankshaft position in order to maintain the closed position of the wastegate.
Even though this method makes it possible to reduce the power loss of the actuator by comparison to the method according to the initially mentioned DE 10 2008 051 818 A1, there is still the disadvantage that pressure pulsations of the exhaust gas might arise with the wastegate in the closed position, which could cause the wastegate to be pressed open slightly for a brief time.
Against this backdrop, at least one object herein is to provide a method for controlling an electrical actuator for a wastegate valve arrangement of an exhaust gas turbocharger in an internal combustion engine, in which the wastegate is exposed to closing forces that are optimally adjusted to the exhaust gas pressures that arise under all operating conditions. It is a further object herein to provide a device for implementing the method. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.